Prior Art
In U.S. Pat. No. 2,791,290, a highspeed embossing apparatus is disclosed which is particularly wellsuited for use in the embossing of relatively deep decorative patterns in molding for furniture, picture frames and the like. This apparatus employs a very hot die (1,000.degree. to 1,200.degree. F. or more) under a substantial pressure to emboss patterns which may have a depth of 1/4 inch or greater into lumber that is usually relatively soft at high speeds (for example, 200 feet per minute). Most prior art devices set forth in the application and cited by the Patent Office typically ran at a temperature of about 1/2 and a speed of about 1/5 of that set forth in U.S. Pat. No. 3,791,290. The apparatus and method set forth in said application employed the very substantially increased die temperatures to achieve a dramatic improvement in production rates and a corresponding reduction in production costs.
In addition to embossing molding, it has long been desirable to be able to emboss a wood grain pattern on articles and particularly sheets or panels. The desirability of embossing such a pattern has increased in recent years since the supply of woods having desirable grain properties has dwindled substantially. The supply of many types of wood which have little or no grain pattern is relatively plentiful, but the use of such wood in furniture, decorative panels, cabinetry, etc., has been limited to situations in which the article would be finished by painting, a plastic laminate, etc.
In order to attempt to utilize woods having poor grain quality, a number of different approaches have been employed. The most widespread process presently in use is a printing process in which ink is imprinted onto the article in a wood grain pattern. In this process, the finish of the panel is controlled by the grain printer, and the manufacturer of the article must attempt to match other wood to the finish of the printed wood.
U.S. Pat. No. 3,294,041 discloses a process in which a die having a pattern of protrusions of substantial height simulating wormholes is heated to a high temperature and urged against the wood product at a very high pressure. A similar process is shown in U.S. pat. No. 3,393,294 in which wormholes are formed by contacting the wood over a substantial period of time by using an endless-tract mounting of the heated protruding elements.
In addition, cold dies have been employed with very substantial pressures to attempt to crush or impress a wood grain pattern into a wooden article. This approach results in chipping and fracturing of the wood fiber, poor grain definition, slow speed and an inability of the impressed grain to visually stand out from the remainder of the wood with a corresponding need to use inks or color fillers to bring out the grain.
U.S. Pat. Nos. 2,703,463 and 3,695,857 disclose low temperature, low speed processes which depend upon high pressure and even support of the panels to effect embossing. A high temperature, high, highspeed embossing apparatus and method similar to that disclosed in my U.S. Pat. No. 3,730,081 is shown in U.S. Pat. No. 3,764,767. In this apparatus and method very high die temperatures on the order of about 1,000.degree. F. are achieved by induction heating and enable embossing of molding at a rate of 200 feet per minute. As was the case with my embossing apparatus, the device of U.S. Pat. No. 3,764,767 is entirely adequate for embossing relatively soft lumbers with a pattern that is relatively gross or coarse in nature.
In my application Ser. No. 440,481, I set forth a process for embossing, or more accurately branding, a wood grain pattern into sheets of material at high, economically feasible production rates. In this process an extremely high temperature die, on the order of about 1,000.degree. F. having an intricate and detailed wood grain pattern thereon, was impressed at relatively low temperature and high speed against panels of lumber to brand a pattern having high definition into the panels. Thus, extremely high die temperatures and relatively low die pressure were employed to achieve a high production output.
While the process of application Ser. No. 440,481, now abandoned, initially met with considerable success, two serious limitations were encountered. It was found that not only is it desirable to be able to brand lumber having poor grain characteristics, but it is also highly desirable to be able to brand particle board and hard board, both of which have no grain characteristics and exhibit extreme surface hardness as compared to most commonly available lumbers. Secondly, it was found that when an intricate and delicate die pattern was employed and heated to extremely high temperatures (1,000.degree. to 1,200.degree. F.), oxidation and wear on the pattern caused rapid degradation of the same with attendant loss of definition in the pattern branded into the lumber. Thus, the operation of dies having delicate patterns at extremely high temperatures was found to cause the die patterns to have an unacceptably short life. This problem was increased when attempting to brand particle board or hard board, which presents an extremely hard surface. Oxidation and wear on the dies under the extremely high temperatures soon caused a degradation of the delicate patterns to a level prohibiting their further use. The cost of etching a steel die 18 inches in diameter and 4 feet in length with an intricate wood grain pattern is substantial ($4000-$5000) and requires that the die be able to be used to brand a very substantial number of panels before it must be replaced.
It is believed that the oxidation and wear phenomena on the die at extremely high temperatures was not observed before in connection with Applicant's method and apparatus as set forth in U.S. Pat. No. 3,730,081 because the patterns employed for embossing molding are inherently rather coarse or gross in nature. Accordingly, there are not normally thin cross-section die protrusions, and oxidation of several thousandths of an inch does not have any appreciable effect on the pattern which is embossed into the molding. Since most moldings are made with soft lumbers, the wear factor was also less than when attempting to brand particle board or hard board. When a die is formed with an intricate wood grain pattern, however, oxidation or wear of a few thousandths of an inch will completely eliminate many of the pattern protrusions creating discontinuities or bald spots in the pattern which are unacceptable. Additionally, carbon build-up on the dies can fill the interstices between protrusions and similarly degrade the die pattern.
Accordingly, it is an object of the present invention to provide a wood grain branding process which can be operated at very high speeds to brand hard board, particle board or lumber with intricate wood grain patterns without causing rapid degradation and deterioration of the die pattern.
Another object of the present invention is to provide a wood grain branding process which can be used for high speed production and has an improved life for its components and particularly the branding die.
It is a further object of the present invention to provide a wood grain branding process which will produce an article having a wood grain branded therein which can be sanded and otherwise finished after branding without destroying the branded pattern.
It is still a further object of the present invention to provide a wood grain branding process which is suitable for branding plywood, particle board and hard board sheets of material.
Another object of the present invention is to provide a wood grain branding process in which the branded grain pattern is discolored during the branding process to simulate the darkened areas of normal wood grain.
Another object of the present invention is to provide a wood grain branding process which is easy to operate, has improved economy, and achieves greater pattern clarity and definition.
Other objects and features of advantage of the wood grain branding process of the present invention will become apparent from or are set forth in detail in the accompanying drawing and the following description of the preferred embodiment.